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<h4>Local Iteration</h4>
<div>
	Local iteration is a simple vertical repetition construct.&nbsp;
	It expands a macro with each number in a user-specified range.&nbsp;
	Each expansion is on a separate line.
</div>
<h4>Tutorial</h4>
<div>
	This mechanism requires two pieces of information to operate:&nbsp;
	a range to iterate over and a macro to expand on each iteration.&nbsp;
	This information is obtained by the mechanism through two <i>named external arguments</i>.&nbsp;
	These arguments are specified as user-defined macros named <b>BOOST_PP_LOCAL_LIMITS</b> and <b>BOOST_PP_LOCAL_MACRO</b>.
</div>
<div>
	<b>BOOST_PP_LOCAL_LIMITS</b> specifies a range of values to iterate over.&nbsp;
	It <i>must</i> expand to a <i>tuple</i> containing two elements--a lower and upper bound.&nbsp;
	Both the upper and lower bounds must be numeric values in the range of <i>0</i> to <b>BOOST_PP_LIMIT_ITERATION</b>.&nbsp;
	For example, if the user wishes a macro to be expanded with numbers ranging from <i>0</i> to <i>10</i>,
	<b>BOOST_PP_LOCAL_LIMITS</b> would be defined like this:
</div>
<div class="code"><pre>
#define BOOST_PP_LOCAL_LIMITS (0, 10)
</pre></div>
<div>
	Note that there is whitespace after the name of the macro.&nbsp;
	The macro <i>does not</i> take <i>two</i> arguments.&nbsp;
	In the case above, if there was no whitespace, a preprocessing error would occur because <i>0</i> and <i>10</i> are invalid identifiers.
</div>
<div>
	Both the upper and lower bounds specified in the <b>BOOST_PP_LOCAL_LIMITS</b> macro are <i>evaluated parameters</i>.&nbsp;
	This implies that they can include simple arithmetic or logical expressions.&nbsp;
	For instance, the above definition could easily have been written like this:
</div>
<div class="code"><pre>
#define N() 5
#define BOOST_PP_LOCAL_LIMITS (0, N() + 5)
</pre></div>
<div>
	Because of this, if the whitespace after the macro name is elided, it is possible for the definition to be syntactically valid:
</div>
<div class="code"><pre>
#define A 0
#define B 10
#define BOOST_PP_LOCAL_LIMITS(A, B)
   // note:  no whitespace   ^
</pre></div>
<div>
	If this happens, an error will occur inside the mechanism when it attempts to use this macro.&nbsp;
	The error messages that result may be obscure, so always remember to include the whitespace.&nbsp;
	A <i>correct</i> version of the above looks like this:
</div>
<div class="code"><pre>
#define A 0
#define B 10
#define BOOST_PP_LOCAL_LIMITS (A, B)
   // note:  has whitespace  ^
</pre></div>
<div>
	<b>BOOST_PP_LOCAL_MACRO</b> is the macro that is expanded by the mechanism.&nbsp;
	This macro is expanded on each iteration with the current number of the iteration.&nbsp;
	It must defined as a unary macro <i>or</i> result in a macro that can be called with one argument:
</div>
<div class="code"><pre>
#define BOOST_PP_LOCAL_MACRO(n) \
   template&lt;&gt; struct sample&lt;n&gt; { }; \
   /**/
</pre></div>
<div>
	...or...
</div>
<div class="code"><pre>
#define SAMPLE(n) \
   template&lt;&gt; struct sample&lt;n&gt; { }; \
   /**/

#define BOOST_PP_LOCAL_MACRO SAMPLE
</pre></div>
<div>
	Once these two macros are defined, the local iteration is initiated by <i>including</i> <b>BOOST_PP_LOCAL_ITERATE</b>().
</div>
<div class="code"><pre>
??=include BOOST_PP_LOCAL_ITERATE()
</pre></div>
<div>
	(The <code>??=</code> token is a trigraph for <code>#</code>.&nbsp;
	I use the trigraph to make it clear that I am <i>including</i> a file rather than defining or expanding a macro, but it is not necessary.&nbsp;
	Even the digraph version, <code>%:</code>, could be used.&nbsp;
	Some compilers do not readily accept trigraphs and digraphs, so keep that in mind.&nbsp;
	Other than that, use whichever one you prefer.)
</div>
<div>
	In order to repeat the <code>sample</code> specialization, the pieces must be put together....
</div>
<div class="code"><pre>
#define BOOST_PP_LOCAL_MACRO(n) \
   template&lt;&gt; struct sample&lt;n&gt; { }; \
   /**/

#define BOOST_PP_LOCAL_LIMITS (0, 10)
??=include BOOST_PP_LOCAL_ITERATE()
</pre></div>
<div>
	This will result in a specialization of <code>sample</code> for each number in the range of <i>0</i> to <i>10</i>.&nbsp;
	The output will look something like this:
</div>
<div class="code"><pre>
template&lt;&gt; struct sample&lt;0&gt; { };
template&lt;&gt; struct sample&lt;1&gt; { };
template&lt;&gt; struct sample&lt;2&gt; { };

// ...

template&lt;&gt; struct sample&lt;10&gt; { };
</pre></div>
<div>
	After the local-iteration is complete, both <b>BOOST_PP_LOCAL_LIMITS</b> and <b>BOOST_PP_LOCAL_MACRO</b> are automatically undefined.&nbsp;
	If the values need to be retained for a future local-iteration, they must be defined indirectly:
</div>
<div class="code"><pre>
#define LIMITS (0, 10)

#define SAMPLE(n) \
   template&lt;&gt; struct sample&lt;n&gt; { }; \
   /**/

#define BOOST_PP_LOCAL_LIMITS LIMITS
#define BOOST_PP_LOCAL_MACRO(n) SAMPLE(n)

??=include BOOST_PP_LOCAL_ITERATE()
</pre></div>
<h4>See Also</h4>
<ul>
	<li><a href="../ref/local_iterate.html">BOOST_PP_LOCAL_ITERATE</a></li>
	<li><a href="../ref/local_limits.html">BOOST_PP_LOCAL_LIMITS</a></li>
	<li><a href="../ref/local_macro.html">BOOST_PP_LOCAL_MACRO</a></li>
</ul>
<div class="sig">- Paul Mensonides</div>
	<hr size="1">
	<div style="margin-left: 0px;">
		<i>� Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
		</br><i>� Copyright Paul Mensonides 2002</i>
	</div>
	<div style="margin-left: 0px;">
		<p><small>Distributed under the Boost Software License, Version 1.0. (See
		accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
		copy at <a href=
		"http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
	</div>
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